Electron optical lens columns are used in order to produce lens effects on electron beams such as in scanning electron microscopes (SEMs) and ion beam (EB) equipment. An example of a lens column used in an SEM is described as an “electrostatic lens” in Japanese Unexamined Patent Application Publication H 6-187901.
However, recently there have been demands for high precision and tighter focusing of electron beams for the purposes of, for example, microlithography processes. Increasing the degree of focus requires high acceleration of the electrons through applying a high voltage. However, this engenders problems in terms of bulky and expensive equipment. Furthermore, high velocity electrons engender the following problems:    (a) Because the electron beam penetrates the surface of the sample, it is no longer suitable for observing the surface.    (b) There will be deleterious effects, such as the sample being destroyed by the electron beam.    (c) With biological samples, the material is nonconductive, and thus electrostatic charge tends to build up. Charged material has an impact on the electric field, adversely affecting the precision of the focus of the electron beam.
However, if it were possible to obtain a compact, high-precision lens column, it would then be possible to shorten the distance between the electrode and the electron beam, making it possible to subject the electron beam to large electric fields even if the acceleration voltage on the electrons is low, and, in turn, making it possible to focus the beam with high precision.
Unfortunately, the electrostatic lenses used in electron optical lens columns require high precision in their placement and dimensions. When lens columns have been made smaller, there has been a tendency for there to be increased error in the positioning and dimensions of the electrostatic lenses, which may lead to reductions in focusing precision.